This invention relates to the securement of flanges, headers, machinery components, bolts and nuts wherein dimensionally uniform clamping forces are desirable, to axial couplings of driven machinery wherein dimensional alignment of such flanges is critical, and to preload pressure adjustment of bearings used in machinery, and particularly to heavy duty taper roller wheel bearings in the transportation industries.
Stressed securement of couplings, flanges, and headers, and adjustment of tapered roller wheel hub bearings has been dependent upon time consuming and inaccurate prior art methods dependent upon gap gauges, digital or dial calipers and indicators, the often used mechanics guesstimate attempting to detect either bearing looseness or excessive preload by means of feeling looseness or stress by the technicians hand, voltage resistant stress materials, a screw thread torque measuring method as a final measure, a screw thread torque measurement from which to measure a final screw thread rotation, use of a dial indicator instrument to measure a perceived degree of free axial movement, or upon dial indicator measure of a perceived zero point from which to measure a final screw thread rotation.
Taper roller bearing failure analysis in the heavy duty transportation industry demonstrates that improper bearing retaining spindle nut adjustment initiates the first component failure resulting in premature wheel end component wear out, successive wheel end component failure, or culminating in vehicle-wheel separation.
Friction variables, a result of dimensional irregularities, lubricant characteristics, contamination, material alloy, finish and smoothness, wear, damage, temperature, galling, and so forth, of wheel end spindle threads, spindle nut threads, and nut face surfaces, collectively render torque-based measurements to very broad adjustment parameters. Without an exact adjustment reference point, bearing preload cannot be set without risk of severely overloading the bearings and precipitating an immediate bearing failure. Consequently, the transportation industry has been forced to adjustment procedures wherein bearings are adjusted loose, but which also reduces useable wheel end component life, results in costly maintenance and operation expenses, and compromises safety.
The industry as a whole has historically chosen to perceive this major safety problem, liability concern, and expense, to be a result of improper maintenance procedures. However, attempts to resolve these issues over the past several decades have lead the industry to adopt a variety of adjustment procedures verifiable by measurement of a minimal free bearing axial endplay. Controllable preload adjustment has not been possible with spindle nuts, measuring devices, and calibration means in present use, and a portion of the industry has attempted to resolve these wheel bearing adjustment issues by resorting to non-adjustable hubs.
The problem lies in that the common practice of endplay verification is badly flawed. Tests demonstrate that the melding of, friction variables of the wheel end components, the heavy weights of the wheel ends, the physics of the inclined planes of the double taper roller bearings, dial indicator placement, and the resultant geometry of exactly how the wheel end is moved, and conclude that verifiable free endplay is only a measure of how far the spindle mounted heavy wheel end can be readily moved in that individual situation, and as such only verifies that the wheel end is loose. A great demonstration of this is to attempt to adjust zero free play, having as an example 0.005 inch verifiable free end play as initially verified by a dial indicator measurement.
By rotating the spindle nut a corresponding degree of rotation in relationship to the spindle screw thread pitch a subsequent verification should then result in zero endplay. The need to repeat this process two or three or four times to obtain a near zero or merely an unknown point where you measure zero immediately becomes evident. The first verification measurement proved to be flawed, and it follows that subsequent verifications are equally flawed. Highly controlled laboratory experiments further verify the illogic and dramatic errors of the concept of verifiable free endplay.
The public safety and liability concerns are so serious that the National Transportation Safety Board has for several years been facilitating efforts and studies of numerous transportation and manufacturing associations to establish a scientific method of preload adjustment and measurement including the development of a test machine to compare new methods to the three piece spindle nut in use for a hundred years. These tests methods are comparative of the popular methods and devices of prior art and do not relate to specific preload pressures in non-laboratory shop and field applications nor resolve the problems. Attempting to sneak up on a desirable and verifiable axial endplay is a very time consuming process and at best the bearings are adjusted loose. At worst the bearings are excessively preloaded.
The prior art method disclosed in U.S. Pat. No. 6,257,078 precisely resolves free play and preload adjustment problems by pre-stressing the axial assembly to remove all friction and elasticity variables from the measurement and adjustment process. The spindle nut is over tightened and a dial indicator is then used to measure the relaxation of the excessive preload by measure of the wheel hub in relation to the spindle as the screw threaded spindle nut is slowly loosened. The problems with this sophisticated and precise adjustment method is that it is dependent on the knowledgeable and time-consuming use of a dial indicator. The dial indicator may be improperly installed and misused by the service personnel and in many shops and in the field an accurate dial indicator and mounting means is not available. Further more, there always exists the possibility that the inner wheel lubricant seal or other wheel end component may interfere with the hubs free axial travel upon the spindle requiring diligent observation of the technician.
In other axial alignment applications, such as securement of headers or alignment of couplings, digital and dial gauges are often used with varying degrees of success as they do not provide a measure of pre-securement stresses affecting accurate and consistent header and flange pressures, or final coupling alignment stresses. Unintended stresses are often first discovered in equipment vibration analysis studies and are further reflected in equipment component useable life and operating efficiency.